This invention relates to X-ray diffraction apparatus in which the focusing method and the parallel beam method can be changed for each other.
X-ray diffraction apparatus may be classified to, in view of X-ray beam divergency, the focusing method and the parallel beam method. In the focusing method, an X-ray beam from an X-ray source is a divergent beam with a predetermined divergence angle and incident upon a sample with a wide irradiation area. Then, the X-ray beam is diffracted by the sample, focused on a receiving slit and thereafter detected by an X-ray detector. In the parallel beam method, on the other hand, an X-ray beam from an X-ray source is made parallel with the use of collimating means, for example a Soller slit or a monochromator, and incident upon a sample. Then, the X-ray beam is diffracted by the sample with keeping the parallel characteristic and is detected by an X-ray detector.
X-ray diffraction apparatus belonging to the focusing method and other X-ray diffraction apparatus belonging to the parallel beam method are usually different from each other. If there is required both of the measurements with the focusing method and with the parallel beam method, the two kinds of the X-ray diffraction apparatus must be prepared. Alternatively, one set of X-ray diffraction apparatus may be used selectively for the focusing method or for the parallel beam method, provided that an exchange of an optical system is required. For example, assuming that a parabolic multilayer mirror is used for making a parallel beam, the focusing method can be changed for the parallel beam method as described below. In the focusing method, an X-ray incident path from an X-ray source to a sample is straight. The change from the focusing method to the parallel beam method requires insertion of the multilayer mirror into the straight incident path. Sine the insertion of the multilayer mirror causes a bend of the X-ray beam path, the sample position must be changed if the X-ray source remains at the same position. Alternatively, the X-ray source position must be changed if the sample remains at the same position. Besides, with the change of the incident optical system, the setting operation for the optical system, i.e., adjustment of the optical axis, must be carried out again.
Then, for obviating the above problems, improved X-ray diffraction apparatus has been developed in which the focusing method and the parallel beam method can be changed for each other substantially without the change of the positional relationship between the X-ray source and the sample. X-ray diffraction apparatus disclosed in Japanese patent publication 9-229879 A (1997) can obtain an X-ray beam for the focusing beam and also an X-ray beam for the parallel beam method with the use of an improved slit device. Other X-ray diffraction apparatus disclosed in Japanese patent publication 11-72595 A (1999) can obtain an X-ray beam for the focusing beam and also an X-ray beam for the parallel beam method with the change between the vertical and horizontal arrangements of a curved-crystal monochromator, noting that the monochromator is used for both of the focusing method and the parallel beam method.
Since the apparatus in Japanese patent publication 9-229879 A (1997) mentioned above obtains the parallel beam by narrowing the opening widths of a plurality of slit devices, there is the problem that the X-ray intensity on the sample becomes weaker in using the parallel beam method. Of course, the apparatus can not use a parabolic multilayer mirror which is superior for making the parallel beam. On the other hand, since the other apparatus disclosed in Japanese patent publication 11-72595 A (1999) mentioned above changes the posture of a curved-crystal monochromator for carrying out the change between the focusing method and the parallel beam method, the setting operation for the optical system is required again. Besides, since the apparatus makes the parallel beam with the curved-crystal monochromator which is in the vertical arrangement, the intensity of the obtained parallel is not sufficient. At any rate, the apparatus also can not use the parabolic multilayer mirror.
It is an object of the present invention to provide X-ray diffraction apparatus which can conduct easy change between the focusing method and the parallel beam method.
It is another object of the present invention to provide X-ray diffraction apparatus which can use, in the parallel beam method, a parabolic multilayer mirror to obtain a sufficient intensity of X-rays with a high resolution.
X-ray diffraction apparatus according to the present invention is for the apparatus in which an X-ray source emits an X-ray beam which is incident upon a sample, diffracted by the sample and detected by an X-ray detector. The X-ray diffraction apparatus comprises: (a) a first incident path along which the X-ray beam is incident upon the sample with a predetermined divergence angle; (b) a second incident path along which the X-ray beam is reflected by a parabolic multilayer mirror to become a parallel beam and thereafter incident upon the sample; (c) a path-selection slit device which can open any one of the first incident path and the second incident path whereas close off the other of the first incident path and the second incident path; (d) an X-ray source in which a position of X-ray generation does not vary independently upon the selection of the first incident path or the second incident path; and (e) a sample holder in which a center position of the sample does not vary independently upon the selection of the first incident path or the second incident path.
The first incident path corresponds to a path for the focusing method, whereas the second incident path corresponds to a path for the parallel beam method. With the present invention, the first and the second incident paths can be selectively changed between the opened and closed off conditions with the use of the path-selection slit device, so that the focusing method and the parallel beam method can be easily changed for each other, requiring no re-setting operation for the optical system. Besides, since the parallel beam method uses the parabolic multilayer mirror, the obtained parallel beam has a good monochromatic property, i.e., a high resolution, and a high intensity as compared with the conventional X-ray diffraction apparatus enabling the change between the focusing method and the parallel beam method.
The X-ray diffraction apparatus according to the present invention may be used in a manner that, for example, the measurement placing priority on the X-ray diffraction intensity can be carried out with the focusing method which uses a direct beam, whereas the precise measurement placing priority on the angular resolution can be carried out with the parallel beam method which uses the parabolic multilayer mirror.
Since the parabolic multilayer mirror has a reflection surface which is made of a synthetic multilayer thin film, the mirror can be synthetically processed to have a small diffraction angle, about several degrees. If the diffraction angle of the mirror is small, the angle formed by the first incident path and the second incident path becomes small advantageously. As a result, the X-ray tube may be kept stationary with the same posture with no problem although the X-ray take-off direction differs between the two incident paths.